Wells are drilled in subsurface formations for the production of hydrocarbons (oil and gas). After drilling, the wellbore is completed typically by lining the wellbore with a casing that is perforated proximate to each oil and gas bearing formation (also referred to herein as the “production zone” or “reservoir”) to extract the fluid from such reservoirs (referred to as “formation fluid”), which typically includes water, oil and/or gas. In multiple production zone wells, sometimes the well is completed with system of packers, monitoring instrumentation, chemical injection valves, inflow control valves and surface control facilities (referred to as “intelligent well” or “intelligent completion”). Intelligent wells are especially useful for areas where intervention costs are high, since they allow operators to remotely monitor and change well conditions without the use of an intervention rig, reducing the total cost of ownership and optimizing production.
Inorganic scale, such as calcium carbonate, results from the precipitation of minerals from water which may be naturally occurring reservoir water or water deriving from water floods. The potential for inorganic scale increases with increased water production. A majority of the wells typically produce hydrocarbons and a certain amount of water that is naturally present in the reservoir. However, under various conditions, such as when the reservoir has been depleted to a sufficient extent, substantial amounts of water present is adjacent formations can penetrate into the reservoir and migrate into the well, or due to other reasons such as the presence of faults in the formation containing the reservoir, particularly in high porosity and high mobility formations. Faults in cement bonds between the casing and formation, holes developed in the casing due to corrosion, etc. may also be the source of water entering the well.
Scale deposition is effected mainly, but not only, by any changes in pressure, temperature, and flow velocity. Scale formation can occur in the reservoir, in the completion, in production lines, and in surface equipment. Common types of inorganic scale comprise: carbonate scales (calcium, magnesium, iron); sulfate scales (calcium, barium and strontium, magnesium); sulfide scales (iron and zinc); iron scales (oxides, carbonates, sulfides); silica scales; and salt scales (calcium, potassium, sodium).
In some areas, produced water presents self-scaling tendency when it flows into the wellbore. In the wellbore, equilibrium conditions that keep inorganic scale from forming or precipitating may change due to changes in pressure and/or temperature. That is, the equilibrium conditions may shift to favor solid-phase formation or precipitation. Unfortunately, the formation or precipitation of inorganic scale can be detrimental to production equipment either downhole or at the surface due to the scale plugging pipes or tubing carrying produced formation fluid. Hence, apparatus and method that can anticipate and diagnose production problems caused by inorganic scales, can predict where inorganic scale may be formed or precipitated in production equipment, can assess the relative effectiveness of various preventative methods (e.g., the efficacy of different inorganic scale inhibitors) under downhole conditions, can provide sufficient warning to develop contingency plans and stage remediation programs, and can prevent its formation would be well received in the oil industry.